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<title>Project IceStorm &ndash; IO Tile Documentation</title>
</head><body>
<h1>Project IceStorm &ndash; IO Tile Documentation</h1>

<p>
<i><a href=".">Project IceStorm</a> aims at documenting the bitstream format of Lattice iCE40
FPGAs and providing simple tools for analyzing and creating bitstream files.
This is work in progress.</i>
</p>

<h2>Span-4 and Span-12 Wires</h2>

<p><a href="iosp.svg"><img alt="IO Tile Span-Wires" style="float:right; padding:1em; padding-top:0; border:0" height="200" src="iosp.svg"></a></p>

<p>
The image on the right shows the span-wires of a left (or right) io cell (click to enlarge).
</p>

<p>
A left/right io cell has 16 connections named <span style="font-family:monospace">span4_vert_t_0</span> to <span style="font-family:monospace">span4_vert_t_15</span> on its top edge and
16 connections named <span style="font-family:monospace">span4_vert_b_0</span> to <span style="font-family:monospace">span4_vert_b_15</span> on its bottom edge. The nets <span style="font-family:monospace">span4_vert_t_0</span>
to <span style="font-family:monospace">span4_vert_t_11</span> are connected to <span style="font-family:monospace">span4_vert_b_4</span> to <span style="font-family:monospace">span4_vert_b_15</span>. The span-4 and span-12 wires
of the adjacent logic cell are connected to the nets <span style="font-family:monospace">span4_horz_0</span> to <span style="font-family:monospace">span4_horz_47</span> and <span style="font-family:monospace">span12_horz_0</span>
to <span style="font-family:monospace">span12_horz_23</span>.
</p>

<p>
A top/bottom io cell has 16 connections named <span style="font-family:monospace">span4_horz_l_0</span> to <span style="font-family:monospace">span4_horz_l_15</span> on its left edge and
16 connections named <span style="font-family:monospace">span4_horz_r_0</span> to <span style="font-family:monospace">span4_horz_r_15</span> on its right edge. The nets <span style="font-family:monospace">span4_horz_l_0</span>
to <span style="font-family:monospace">span4_horz_l_11</span> are connected to <span style="font-family:monospace">span4_horz_r_4</span> to <span style="font-family:monospace">span4_horz_r_15</span>. The span-4 and span-12 wires
of the adjacent logic cell are connected to the nets <span style="font-family:monospace">span4_vert_0</span> to <span style="font-family:monospace">span4_vert_47</span> and <span style="font-family:monospace">span12_vert_0</span>
to <span style="font-family:monospace">span12_vert_23</span>.
</p>

<p>
The vertical span4 wires of left/right io cells are connected "around the corner" to the horizontal span4 wires of the top/bottom
io cells. For example <span style="font-family:monospace">span4_vert_b_0</span> of IO cell (0 1) is connected to <span style="font-family:monospace">span4_horz_l_0</span> (<span style="font-family:monospace">span4_horz_r_4</span>)
of IO cell (1 0).
</p>

<p>
Note that unlike the span-wires connection LOGIC and RAM tiles, the span-wires
connecting IO tiles to each other are not pairwise crossed out.
</p>

<h2>IO Blocks</h2>

<p>
Each IO tile contains two IO blocks. Each IO block essentially implements the <span style="font-family:monospace">SB_IO</span>
primitive from the Lattice iCE Technology Library.
Some inputs are shared between the two IO blocks. The following table lists how the
wires in the logic tile map to the <span style="font-family:monospace">SB_IO</span> primitive ports:
</p>

<table class="ctab">
<tr><th>SB_IO Port</th><th>IO Block 0</th><th>IO Block 1</th></tr>
<tr><td>D_IN_0</td><td><span style="font-family:monospace">io_0/D_IN_0</span></td><td><span style="font-family:monospace">io_1/D_IN_0</span></td></tr>
<tr><td>D_IN_1</td><td><span style="font-family:monospace">io_0/D_IN_1</span></td><td><span style="font-family:monospace">io_1/D_IN_1</span></td></tr>
<tr><td>D_OUT_0</td><td><span style="font-family:monospace">io_0/D_OUT_0</span></td><td><span style="font-family:monospace">io_1/D_OUT_0</span></td></tr>
<tr><td>D_OUT_1</td><td><span style="font-family:monospace">io_0/D_OUT_1</span></td><td><span style="font-family:monospace">io_1/D_OUT_1</span></td></tr>
<tr><td>OUTPUT_ENABLE</td><td><span style="font-family:monospace">io_0/OUT_ENB</span></td><td><span style="font-family:monospace">io_1/OUT_ENB</span></td></tr>
<tr><td>CLOCK_ENABLE</td><td colspan="2"><span style="font-family:monospace">io_global/cen</span></td></tr>
<tr><td>INPUT_CLK</td><td colspan="2"><span style="font-family:monospace">io_global/inclk</span></td></tr>
<tr><td>OUTPUT_CLK</td><td colspan="2"><span style="font-family:monospace">io_global/outclk</span></td></tr>
<tr><td>LATCH_INPUT_VALUE</td><td colspan="2"><span style="font-family:monospace">io_global/latch</span></td></tr>
</table>

<p>
Like the inputs to logic cells, the inputs to IO blocks are routed to the IO block via a two-stage process. A signal
is first routed to one of 16 local tracks in the IO tile and then from the local track to the IO block.
</p>

<p>
The <span style="font-family:monospace">io_global/latch</span> signal is shared among all IO tiles on an edge of the chip and is driven by <span style="font-family:monospace">fabout</span>
from one dedicated IO tile on that edge. For the HX1K chips the tiles driving the <span style="font-family:monospace">io_global/latch</span> signal are:
(0, 7), (13, 10), (5, 0), and (8, 17)
</p>

<p>
A logic tile sends the output of its eight logic cells to its neighbour tiles. An IO tile does the same thing with the four <span style="font-family:monospace">D_IN</span>
signals created by its two IO blocks. The <span style="font-family:monospace">D_IN</span> signals map to logic function indices as follows:
</p>

<table class="ctab">
<tr><th>Function Index</th><th>D_IN Wire</th></tr>
<tr><td>0</td><td><span style="font-family:monospace">io_0/D_IN_0</span></td></tr>
<tr><td>1</td><td><span style="font-family:monospace">io_0/D_IN_1</span></td></tr>
<tr><td>2</td><td><span style="font-family:monospace">io_1/D_IN_0</span></td></tr>
<tr><td>3</td><td><span style="font-family:monospace">io_1/D_IN_1</span></td></tr>
<tr><td>4</td><td><span style="font-family:monospace">io_0/D_IN_0</span></td></tr>
<tr><td>5</td><td><span style="font-family:monospace">io_0/D_IN_1</span></td></tr>
<tr><td>6</td><td><span style="font-family:monospace">io_1/D_IN_0</span></td></tr>
<tr><td>7</td><td><span style="font-family:monospace">io_1/D_IN_1</span></td></tr>
</table>

<p>
For example the signal <span style="font-family:monospace">io_1/D_IN_0</span> in IO tile (0, 5) can be seen as <span style="font-family:monospace">neigh_op_lft_2</span> and <span style="font-family:monospace">neigh_op_lft_6</span> in LOGIC tile (1, 5).
</p>

<p>
Each IO Tile has 2 <span style="font-family:monospace">NegClk</span> configuration bits, suggesting that the
clock signals can be inverted independently for the the two IO blocks in the
tile. However, the Lattice tools refuse to pack two IO blocks with different clock
polarity into the same IO tile. In our tests we only managed to either set or clear
both NegClk bits.
</p>

<p>
Each IO block has two <span style="font-family:monospace">IoCtrl IE</span> bits that enable the input buffers and
two <span style="font-family:monospace">IoCtrl REN</span> bits that enable the pull up resistors. Both bits are active
low, i.e. an unused IO tile will have both IE bits set and both REN bits cleared (the
default behavior is to enable pullup resistors on all unused pins). Note that
<span style="font-family:monospace">icebox_explain.py</span> will ignore all IO tiles that only have the two <span style="font-family:monospace">IoCtrl
IE</span> bits set.
</p>

<p>
However, the <span style="font-family:monospace">IoCtrl IE_0/IE_1</span> and <span style="font-family:monospace">IoCtrl REN_0/REN_1</span> do not
necessarily configure the IO PIN that are connected to the IO block in the same tile,
and if they do the numbers (0/1) do not necessarily match. As a general rule, the pins
on the right and bottom side of the chips match up with the IO blocks and for the pins
on the left and top side the numbers must be swapped. But in some cases the IO block
and the set of <span style="font-family:monospace">IE/REN</span> are not even located in the same tile. The following
table lists the correlation between IO blocks and <span style="font-family:monospace">IE/REN</span> bits for the
1K chip:
</p>

<table class="xtab">
<tr><td>

<table class="ctab">
<tr><th>IO Block</th><th>IE/REN Block</th></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 14 1</td><td style="text-align:center">0 14 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 14 0</td><td style="text-align:center">0 14 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 13 1</td><td style="text-align:center">0 13 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 13 0</td><td style="text-align:center">0 13 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 12 1</td><td style="text-align:center">0 12 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 12 0</td><td style="text-align:center">0 12 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 11 1</td><td style="text-align:center">0 11 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 11 0</td><td style="text-align:center">0 11 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 10 1</td><td style="text-align:center">0 10 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0 10 0</td><td style="text-align:center">0 10 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  9 1</td><td style="text-align:center">0  9 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  9 0</td><td style="text-align:center">0  9 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  8 1</td><td style="text-align:center">0  8 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  8 0</td><td style="text-align:center">0  8 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  6 1</td><td style="text-align:center">0  6 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  6 0</td><td style="text-align:center">0  6 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  5 1</td><td style="text-align:center">0  5 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  5 0</td><td style="text-align:center">0  5 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  4 1</td><td style="text-align:center">0  4 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  4 0</td><td style="text-align:center">0  4 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  3 1</td><td style="text-align:center">0  3 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  3 0</td><td style="text-align:center">0  3 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  2 1</td><td style="text-align:center">0  2 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0  2 0</td><td style="text-align:center">0  2 1</td></tr>
</table>

</td><td>

<table class="ctab">
<tr><th>IO Block</th><th>IE/REN Block</th></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 1 0 0</td><td style="text-align:center"> 1 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 1 0 1</td><td style="text-align:center"> 1 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 2 0 0</td><td style="text-align:center"> 2 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 2 0 1</td><td style="text-align:center"> 2 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 3 0 0</td><td style="text-align:center"> 3 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 3 0 1</td><td style="text-align:center"> 3 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 4 0 0</td><td style="text-align:center"> 4 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 4 0 1</td><td style="text-align:center"> 4 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 5 0 0</td><td style="text-align:center"> 5 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 5 0 1</td><td style="text-align:center"> 5 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 6 0 1</td><td style="text-align:center"> 6 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 7 0 0</td><td style="text-align:center"> 6 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 6 0 0</td><td style="text-align:center"> 7 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 7 0 1</td><td style="text-align:center"> 7 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 8 0 0</td><td style="text-align:center"> 8 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 8 0 1</td><td style="text-align:center"> 8 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 9 0 0</td><td style="text-align:center"> 9 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 9 0 1</td><td style="text-align:center"> 9 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">10 0 0</td><td style="text-align:center">10 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">10 0 1</td><td style="text-align:center">10 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">11 0 0</td><td style="text-align:center">11 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">11 0 1</td><td style="text-align:center">11 0 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">12 0 0</td><td style="text-align:center">12 0 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">12 0 1</td><td style="text-align:center">12 0 1</td></tr>
</table>

</td><td>

<table class="ctab">
<tr><th>IO Block</th><th>IE/REN Block</th></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  1 0</td><td style="text-align:center">13  1 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  1 1</td><td style="text-align:center">13  1 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  2 0</td><td style="text-align:center">13  2 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  2 1</td><td style="text-align:center">13  2 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  3 1</td><td style="text-align:center">13  3 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  4 0</td><td style="text-align:center">13  4 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  4 1</td><td style="text-align:center">13  4 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  6 0</td><td style="text-align:center">13  6 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  6 1</td><td style="text-align:center">13  6 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  7 0</td><td style="text-align:center">13  7 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  7 1</td><td style="text-align:center">13  7 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  8 0</td><td style="text-align:center">13  8 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  8 1</td><td style="text-align:center">13  8 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  9 0</td><td style="text-align:center">13  9 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13  9 1</td><td style="text-align:center">13  9 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 11 0</td><td style="text-align:center">13 10 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 11 1</td><td style="text-align:center">13 10 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 12 0</td><td style="text-align:center">13 11 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 12 1</td><td style="text-align:center">13 11 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 13 0</td><td style="text-align:center">13 13 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 13 1</td><td style="text-align:center">13 13 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 14 0</td><td style="text-align:center">13 14 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 14 1</td><td style="text-align:center">13 14 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 15 0</td><td style="text-align:center">13 15 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">13 15 1</td><td style="text-align:center">13 15 1</td></tr>
</table>

</td><td>

<table class="ctab">
<tr><th>IO Block</th><th>IE/REN Block</th></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">12 17 1</td><td style="text-align:center">12 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">12 17 0</td><td style="text-align:center">12 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">11 17 1</td><td style="text-align:center">11 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">11 17 0</td><td style="text-align:center">11 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">10 17 1</td><td style="text-align:center"> 9 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">10 17 0</td><td style="text-align:center"> 9 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 9 17 1</td><td style="text-align:center">10 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 9 17 0</td><td style="text-align:center">10 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 8 17 1</td><td style="text-align:center"> 8 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 8 17 0</td><td style="text-align:center"> 8 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 7 17 1</td><td style="text-align:center"> 7 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 7 17 0</td><td style="text-align:center"> 7 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 6 17 1</td><td style="text-align:center"> 6 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 5 17 1</td><td style="text-align:center"> 5 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 5 17 0</td><td style="text-align:center"> 5 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 4 17 1</td><td style="text-align:center"> 4 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 4 17 0</td><td style="text-align:center"> 4 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 3 17 1</td><td style="text-align:center"> 3 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 3 17 0</td><td style="text-align:center"> 3 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 2 17 1</td><td style="text-align:center"> 2 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 2 17 0</td><td style="text-align:center"> 2 17 0</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 1 17 1</td><td style="text-align:center"> 1 17 1</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center"> 1 17 0</td><td style="text-align:center"> 1 17 0</td></tr>
</table>

</table>

<p>
When an input pin pair is used as LVDS pair (IO standard
<span style="font-family:monospace">SB_LVDS_INPUT</span>, bank 3 / left edge only), then the four bits
<span style="font-family:monospace">IoCtrl IE_0/IE_1</span> and <span style="font-family:monospace">IoCtrl REN_0/REN_1</span> are all set, as well
as the <span style="font-family:monospace">IoCtrl LVDS</span> bit.
</p>

<p>
In the iCE 8k devices the <span style="font-family:monospace">IoCtrl IE</span> bits are active high. So an unused
IO tile on an 8k chip has all bits cleared.
</p>

<h2>Global Nets</h2>

<p>
iCE40 FPGAs have 8 global nets. Each global net can be driven directly from an
IO pin.  In the FPGA bitstream, routing of external signals to global nets is
not controlled by bits in the IO tile. Instead bits that do not belong to any
tile are used. In IceBox nomenclature such bits are called "extra bits".
</p>

<p>
The following table lists which pins / IO blocks may be used to drive
which global net, and what <span style="font-family:monospace">.extra</span> statements in the IceStorm ASCII file
format to represent the corresponding configuration bits:
</p>


<table class="ctab">
<tr><th>Glb Net</th><th>Pin<br/>(HX1K-TQ144)</th><th>IO Tile +<br/>Block #</th><th>IceBox Statement</th></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">0</td><td style="text-align:center"> 93</td><td style="text-align:center">13  8  1</td><td style="text-align:center">.extra_bit 0 330 142</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">1</td><td style="text-align:center"> 21</td><td style="text-align:center"> 0  8  1</td><td style="text-align:center">.extra_bit 0 331 142</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">2</td><td style="text-align:center">128</td><td style="text-align:center"> 7 17  0</td><td style="text-align:center">.extra_bit 1 330 143</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">3</td><td style="text-align:center"> 50</td><td style="text-align:center"> 7  0  0</td><td style="text-align:center">.extra_bit 1 331 143</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">4</td><td style="text-align:center"> 20</td><td style="text-align:center"> 0  9  0</td><td style="text-align:center">.extra_bit 1 330 142</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">5</td><td style="text-align:center"> 94</td><td style="text-align:center">13  9  0</td><td style="text-align:center">.extra_bit 1 331 142</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">6</td><td style="text-align:center"> 49</td><td style="text-align:center"> 6  0  1</td><td style="text-align:center">.extra_bit 0 330 143</td></tr>
<tr style="white-space: pre; font-family: monospace"><td style="text-align:center">7</td><td style="text-align:center">129</td><td style="text-align:center"> 6 17  1</td><td style="text-align:center">.extra_bit 0 331 143</td></tr>
</table>

<p>
Signals internal to the FPGA can also be routed to the global nets. This is done by routing the signal
to the <span style="font-family:monospace">fabout</span> net on an IO tile. The same set of I/O tiles is used for this, but in this
case each of the I/O tiles corresponds to a different global net:
</p>

<table class="ctab">
<tr><th>Glb Net</th>
<td style="text-align:center">0</td>
<td style="text-align:center">1</td>
<td style="text-align:center">2</td>
<td style="text-align:center">3</td>
<td style="text-align:center">4</td>
<td style="text-align:center">5</td>
<td style="text-align:center">6</td>
<td style="text-align:center">7</td></tr>
<tr><th>IO Tile</th>
<td style="white-space: pre; font-family: monospace; text-align:center"> 7  0</td>
<td style="white-space: pre; font-family: monospace; text-align:center"> 7 17</td>
<td style="white-space: pre; font-family: monospace; text-align:center">13  9</td>
<td style="white-space: pre; font-family: monospace; text-align:center"> 0  9</td>
<td style="white-space: pre; font-family: monospace; text-align:center"> 6 17</td>
<td style="white-space: pre; font-family: monospace; text-align:center"> 6  0</td>
<td style="white-space: pre; font-family: monospace; text-align:center"> 0  8</td>
<td style="white-space: pre; font-family: monospace; text-align:center">13  8</td></tr>
</table>

<p><a href="colbuf.svg"><img alt="Column Buffers" style="float:right; padding:1em; padding-top:0; border:0" height="200" src="colbuf.svg"></a></p>

<h3>Column Buffer Control Bits</h3>

<p>
Each LOGIC, IO, and RAMB tile has 8 ColBufCtrl bits, one for each global net. In most tiles this
bits have no function, but in tiles in rows 4, 5, 12, and 13 (for RAM columns: rows 3, 5, 11, and 13) this bits
control which global nets are driven to the column of tiles below and/or above that tile (including that tile),
as illustrated in the image to the right (click to enlarge).
</p>

<p>
In 8k chips the rows 8, 9, 24, and 25 contain the column buffers. 8k RAMB and
RAMT tiles can control column buffers, so the pattern looks the same for RAM, LOGIC, and
IO columns.
</p>

<h2>Warmboot</h2>

<p>
The <span style="font-family:monospace">SB_WARMBOOT</span> primitive in iCE40 FPGAs has three inputs and no outputs. The three inputs of that cell
are driven by the <span style="font-family:monospace">fabout</span> signal from three IO tiles. In HX1K chips the tiles connected to the
<span style="font-family:monospace">SB_WARMBOOT</span> primitive are:
</p>

<table class="ctab">
<tr><th>Warmboot Pin</th><th>IO Tile</th></tr>
<tr><td>BOOT</td><td><span style="font-family:monospace">12 0</span></td></tr>
<tr><td>S0</td><td><span style="font-family:monospace">13 1</span></td></tr>
<tr><td>S1</td><td><span style="font-family:monospace">13 2</span></td></tr>
</table>

<h2>PLL Cores</h2>

<p>
The PLL primitives in iCE40 FPGAs are configured using the <span style="font-family:monospace">PLLCONFIG_*</span>
bits in the IO tiles. The configuration for a single PLL cell is spread out
over many IO tiles. For example, the PLL cell in the 1K chip are configured as
follows (bits listed from LSB to MSB):
</p>

<table class="xtab">
<tr><td>

<table class="ctab">
<tr><th>IO Tile</th><th>Config Bit</th><th>SB_PLL40_* Parameter</th></tr>

<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_5</span></td><td rowspan="3">Select PLL Type:<br/>
000 = DISABLED<br/>
010 = SB_PLL40_PAD<br/>
100 = SB_PLL40_2_PAD<br/>
110 = SB_PLL40_2F_PAD<br/>
011 = SB_PLL40_CORE<br/>
111 = SB_PLL40_2F_CORE</td></tr>
<tr><td>0 5</td><td><span style="font-family:monospace">PLLCONFIG_1</span></td></tr>
<tr><td>0 5</td><td><span style="font-family:monospace">PLLCONFIG_3</span></td></tr>

<tr><td>0 5</td><td><span style="font-family:monospace">PLLCONFIG_5</span></td><td rowspan="3"><span style="font-family:monospace">FEEDBACK_PATH</span><br/>
000 = "DELAY"<br/>
001 = "SIMPLE"<br/>
010 = "PHASE_AND_DELAY"<br/>
110 = "EXTERNAL"</td></tr>
<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_9</span></td></tr>
<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_1</span></td></tr>

<tr><td>0 4</td><td><span style="font-family:monospace">PLLCONFIG_4</span></td><td rowspan="1"><span style="font-family:monospace">DELAY_ADJUSTMENT_MODE_FEEDBACK</span><br/>
0 = "FIXED"<br/>
1 = "DYNAMIC"</td></tr>

<tr><td>0 4</td><td><span style="font-family:monospace">PLLCONFIG_9</span></td><td rowspan="1"><span style="font-family:monospace">DELAY_ADJUSTMENT_MODE_RELATIVE</span><br/>
0 = "FIXED"<br/>
1 = "DYNAMIC"</td></tr>

<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_6</span></td><td rowspan="2"><span style="font-family:monospace">PLLOUT_SELECT<br/>PLLOUT_SELECT_PORTA</span><br/>
00 = "GENCLK"<br/>
01 = "GENCLK_HALF"<br/>
10 = "SHIFTREG_90deg"<br/>
11 = "SHIFTREG_0deg"</td></tr>
<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_7</span></td></tr>

<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_2</span></td><td rowspan="2"><span style="font-family:monospace">PLLOUT_SELECT_PORTB</span><br/>
00 = "GENCLK"<br/>
01 = "GENCLK_HALF"<br/>
10 = "SHIFTREG_90deg"<br/>
11 = "SHIFTREG_0deg"</td></tr>
<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_3</span></td></tr>

<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_4</span></td><td rowspan="1"><span style="font-family:monospace">SHIFTREG_DIV_MODE</span></td></tr>

<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_8</span></td><td rowspan="1"><span style="font-family:monospace">TEST_MODE</span></td></tr>

<tr><td>0 5</td><td><span style="font-family:monospace">PLLCONFIG_2</span></td><td rowspan="1">Enable ICEGATE for <span style="font-family:monospace">PLLOUTGLOBALA</span></td></tr>
<tr><td>0 5</td><td><span style="font-family:monospace">PLLCONFIG_4</span></td><td rowspan="1">Enable ICEGATE for <span style="font-family:monospace">PLLOUTGLOBALB</span></td></tr>

</table></td><td>

<table class="ctab">
<tr><th>IO Tile</th><th>Config Bit</th><th>SB_PLL40_* Parameter</th></tr>

<tr><td>0 3</td><td><span style="font-family:monospace">PLLCONFIG_9</span></td><td rowspan="4"><span style="font-family:monospace">FDA_FEEDBACK</span></td></tr>
<tr><td>0 4</td><td><span style="font-family:monospace">PLLCONFIG_1</span></td></tr>
<tr><td>0 4</td><td><span style="font-family:monospace">PLLCONFIG_2</span></td></tr>
<tr><td>0 4</td><td><span style="font-family:monospace">PLLCONFIG_3</span></td></tr>

<tr><td>0 5</td><td><span style="font-family:monospace">PLLCONFIG_5</span></td><td rowspan="4"><span style="font-family:monospace">FDA_RELATIVE</span></td></tr>
<tr><td>0 4</td><td><span style="font-family:monospace">PLLCONFIG_6</span></td></tr>
<tr><td>0 4</td><td><span style="font-family:monospace">PLLCONFIG_7</span></td></tr>
<tr><td>0 4</td><td><span style="font-family:monospace">PLLCONFIG_8</span></td></tr>

<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_1</span></td><td rowspan="4"><span style="font-family:monospace">DIVR</span></td></tr>
<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_2</span></td></tr>
<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_3</span></td></tr>
<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_4</span></td></tr>

<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_5</span></td><td rowspan="7"><span style="font-family:monospace">DIVF</span></td></tr>
<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_6</span></td></tr>
<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_7</span></td></tr>
<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_8</span></td></tr>
<tr><td>0 1</td><td><span style="font-family:monospace">PLLCONFIG_9</span></td></tr>
<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_1</span></td></tr>
<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_2</span></td></tr>

<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_3</span></td><td rowspan="3"><span style="font-family:monospace">DIVQ</span></td></tr>
<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_4</span></td></tr>
<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_5</span></td></tr>

<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_6</span></td><td rowspan="3"><span style="font-family:monospace">FILTER_RANGE</span></td></tr>
<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_7</span></td></tr>
<tr><td>0 2</td><td><span style="font-family:monospace">PLLCONFIG_8</span></td></tr>

</table>
</table>

<p>
The PLL inputs are routed to the PLL via the <span style="font-family:monospace">fabout</span> signal from various IO tiles. The non-clock
PLL outputs are routed via otherwise unused <span style="font-family:monospace">neigh_op_*</span> signals in fabric corners. For example in case
of the 1k chip:
</p>

<table class="ctab">
<tr><th>Tile</th><th>Net-Segment</th><th>SB_PLL40_* Port Name</th></tr>
<tr><td>0 1</td><td><span style="font-family:monospace">fabout</span></td><td rowspan="1"><span style="font-family:monospace">REFERENCECLK</span></td></tr>
<tr><td>0 2</td><td><span style="font-family:monospace">fabout</span></td><td rowspan="1"><span style="font-family:monospace">EXTFEEDBACK</span></td></tr>
<tr><td>0 4</td><td><span style="font-family:monospace">fabout</span></td><td rowspan="8"><span style="font-family:monospace">DYNAMICDELAY</span></td></tr>
<tr><td>0 5</td><td><span style="font-family:monospace">fabout</span></td></tr>
<tr><td>0 6</td><td><span style="font-family:monospace">fabout</span></td></tr>
<tr><td>0 10</td><td><span style="font-family:monospace">fabout</span></td></tr>
<tr><td>0 11</td><td><span style="font-family:monospace">fabout</span></td></tr>
<tr><td>0 12</td><td><span style="font-family:monospace">fabout</span></td></tr>
<tr><td>0 13</td><td><span style="font-family:monospace">fabout</span></td></tr>
<tr><td>0 14</td><td><span style="font-family:monospace">fabout</span></td></tr>
<tr><td>1 1</td><td><span style="font-family:monospace">neigh_op_bnl_1</span></td><td rowspan="1"><span style="font-family:monospace">LOCK</span></td></tr>
<tr><td>1 0</td><td><span style="font-family:monospace">fabout</span></td><td rowspan="1"><span style="font-family:monospace">BYPASS</span></td></tr>
<tr><td>2 0</td><td><span style="font-family:monospace">fabout</span></td><td rowspan="1"><span style="font-family:monospace">RESETB</span></td></tr>
<tr><td>5 0</td><td><span style="font-family:monospace">fabout</span></td><td rowspan="1"><span style="font-family:monospace">LATCHINPUTVALUE</span></td></tr>
<tr><td>12 1</td><td><span style="font-family:monospace">neigh_op_bnr_3</span></td><td rowspan="1"><span style="font-family:monospace">SDO</span></td></tr>
<tr><td>4 0</td><td><span style="font-family:monospace">fabout</span></td><td rowspan="1"><span style="font-family:monospace">SDI</span></td></tr>
<tr><td>3 0</td><td><span style="font-family:monospace">fabout</span></td><td rowspan="1"><span style="font-family:monospace">SCLK</span></td></tr>
</table>

<p>
The PLL clock outputs are fed directly into the input path of certain IO tiles.
In case of the 1k chip the PORTA clock is fed into PIO 1 of IO Tile (6 0) and
the PORTB clock is fed into PIO 0 of IO Tile (7 0). Because of this, those two
PIOs can only be used as output Pins by the FPGA fabric when the PLL ports
are being used.
</p>

<p>
The input path that are stolen are also used to implement the ICEGATE function.
If the input pin type of the input path being stolen is set to
<span style="font-family:monospace">PIN_INPUT_LATCH</span>, then the ICEGATE
function is enabled for the corresponding <span style="font-family:monospace">CORE</span>
output of the PLL.
</p>

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